After being kidnapped by the cult Gorgom on the night of their 19th
birthday, stepbrothers Minami Kotaro and Nobuhiko Akizuki were submitted
to a cyborg surgery with the purpose of becoming the candidates for the
next Gorgom Creation King. Both of them are called Century Kings and are
destined to best each other in a final battle - whoever wins will become
the next Creation King.

Kotaro escaped before getting brainwashed (which is the final step in
the surgery), with help from his foster father, and turned against
Gorgom. He soon finds out the horrific truth from his stepfather: Gorgom
originally killed his true parents and, since both Kotaro and Nobuhiko
were born on the day of a solar eclipse, referred as "Black Sun" and
"Shadow Moon". Kotaro, taking on the name of Kamen Rider BLACK, was
determined to rescue his stepbrother from Gorgom while protecting Japan.
However, later in the series, Nobuhiko emerged as Shadow Moon to fight
Kotaro with the survivor becoming the next Creation King.

With its very dramatic storyline and its twist of the Kamen Rider having
a tragic relationship with his arch-nemesis, this installment not only
became very popular in Japan, but also in the several other countries
where it was aired. The series is often regarded as a classic and is
considered by many as the best Kamen Rider show of the late 80's. Kamen
Rider BLACK RX was a direct sequel to this series.